MENDELISM AND SELECTION 



The larger animals then produce larger average 

 offspring and vice versa. An examination of 

 Fig. 40 will show why. Animals of the same ab- 

 solute size are there placed in the same vertical 

 row. If, now, one selects from the mixed popu- 

 lation only the largest individuals, he will nat- 

 urally secure representatives of only two or 

 three pure lines, viz. of those lines which are 

 characterized by the largest average size, and 

 which, therefore, will produce large average 

 offspring. If on the other hand he selects 

 extremely small individuals, he will secure 

 representatives of only the smallest races, 

 which naturally will produce small offspring, 

 so that selection seems to be effective in modi- 

 fying racial size, but in reality it does this by 

 sorting out the elementary constituents of the 

 race. 



It is impossible to deny the soundness of 

 the reasoning of Johannsen and Jennings. It 

 is perfectly clear that the effects of selection 

 should be more immediate and much greater 

 in the case of a mixed race than in that of a 

 pure line, but is it certain, as assumed by 

 them, that selection is wholly without effect in 



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